You can use the below to find some basic information about the hardware your Linux system is installed on:

How much RAM is installed and how much of it is in use (megabytes).
It will also include swap memory:
$ free -m
total used free shared buffers cached
Mem: 3949 3189 760 0 599 1594
-/+ buffers/cache: 995 2954
Swap: 16386 109 16277
Processor type:
$ cat /proc/cpuinfo
Check the size of the hard drive and what hard drives are available in the system.
This command will also list USB drives and sticks. You need root permissions to execute the fdisk command:
$ sudo fdisk -l | grep GB
Disk /dev/sda: 42.9 GB, 42949672960 bytes
Disk /dev/sdb: 107.3 GB, 107374182400 bytes